1. Field of the Invention
The present invention relates to a system for producing parts/substrate assemblies in each of which a plurality of kinds of parts or components are mounted on a substrate. More particularly, it relates to a parts/substrate assembly producing system well suited to mount electronic parts such as LSIs, on substrates such as ceramic substrates and printed circuit boards for use in computers etc.
2. Description of the Related Art
An assembly line for printed circuit boards for use in computers etc. has the feature that the printed circuit boards and electronic parts (for example, LSIs) are of various kinds. With note taken of this feature, the inventors consider it favorable to first put the electronic parts together as parts kits separately for the individual substrates on which the parts are to be mounted, and to supply each parts kit to an apparatus which mounts the parts of the kit on the associated substrate.
Such an expedient for supplying the parts is appropriate in a case where the parts are not prone to failure or damage in a production line. By way of example, it is difficult to cause lead pin type LSIs, whose integration density is not very high, to become defective in the production line, so that the supplying expedient is applicable thereto.
Meanwhile, with further progress in the packaging technology of large-sized computers, printed circuit boards constituting electronic circuits have been shifting to ceramic substrates capable of higher-density packaging. Also for LSIs which are mounted on the ceramic substrate, a connection method based on solder bumps has consequently been replacing the conventional lead pin type in order to secure a larger number of connection points.
Therefore, a process for mounting electronic parts or components such as the LSIs on the ceramic substrate becomes very complicated. By way of example, at the step of fabricating for the LSI, solder balls serve to connect this LSI to the substrate, and solder balls in the number of 500.about.800 need to be regularly arranged on a chip of about 10 mm-square! after the LSI received by a factory has been detached from a baby board. The execution of such microfabrication poses the problem that fabrication defects might arise in the LSI, so even when the LSIs for a lot of work are complete at the time of receipt, the shortage of the parts or LSIs might occur during the course of the process. On the other hand, it is sometimes impossible to receive the substrates and the LSIs within the predetermined time limit of delivery, for reasons such as difficulties with the technique of ceramic fabrication, etc.
As stated before, the substrate assembling technique requires as a prerequisite the conditions that the substrates and the LSIs which correspond to one lot of work for building one or more computers are complete at the time of starting the process, and that no damage to the LSIs takes place within the process.
In the case of applying the above method to a ceramic substrate assembling production system, therefore, it is apprehended that half-finished substrate assemblies will increase due to waiting for the supplement of the missing LSIs (ascribable to the defective LSIs), and that enormous amounts of manual labor will be necessitated for irregular disposals for coping with a lot which has undergone the shortage of the LSIs, resulting in the disorder of the process.
Besides, since the ceramic substrates and the LSIs are very expensive, reduction in the number of half-finished substrate assemblies and aid in the production system capable of delivering the products in a short time period become very important for curtailing a product cost.
Further, as stated before, the LSI needs to be formed with the solder balls on its surface after the introduction thereof into the production process. In this regard, there is the problem in the process that, when a certain time limit is exceeded from the formation of the solder balls till the mounting of the LSI and the reflow of the LSI bearing substrate, inferior soldering is incurred as a result of the oxidation of the soldering surface, etc. Therefore, how the synchronization between the ceramic substrate and the LSIs is achieved for the timely supply of the LSI parts becomes important for production control and quality control.